K56flex

K56flex (originally called the K56Plus) was a modem chipset[?] from Rockwell that gave users the possibility of receiving data on ordinary phone lines at 56 Kbps (thousand bits per second) as opposed to the previous maximum of 33.6 Kbps. K56flex was similar to the US Robotics X2[?] chipset.

After a brief period of competition K56flex and X2 were replaced by the ITU V.90 standard.

56 Kbps transmission exploits the fact that most telephone exchanges are interconnected with digital lines and so can use a transmission technique on a twisted pair line that avoids the usual digital-to-analog conversion.

The actual improvement in transmission rates was often marginal.